DE3032790A1 - MOTOR PROTECTION CIRCUIT - Google Patents

Description

Applicant: ■ Stuttgart, August 18, 1980

John F. Walton P3919

6853 Strata Street

McLean, Virginia 22101, USA

Representative;

Kohler - Schwindling - Späth
Patent attorneys
Hohentwielstrasse 41

7000 Stuttgart 1

Motor protection circuit

The invention relates to an arrangement for the protection of electric motors, which via a power switching element with are connectable to a power source. In particular, the invention relates to a motor protection circuit which Current or voltage states detected on the feed side of the power switching element.

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Common motor protection arrangements cover different ones Fault conditions in multi-phase switchgear such as undervoltage, Overvoltage,! Phase shift or phase reversal, missing phase, earth fault and the like Failure. If one or more of these faults is detected, the protective arrangement trips the power switching element and thereby separates the motor from the power source, to the motor against the Hetz and the mains against the Protect engine

In the case of the known protection arrangements, the power switching element is only monitored on the network side, so that the actual Conditions on the engine side are often not detected or only detected after damage has occurred. Damage like For example, a wire break between the power switching element and the motor are only detected when the motor Sustained damage due to two-phase run (or single-phase run in a two-Hiasen system). Something like that can occur if a contact bridge of the power switching element is broken or a contact is burned is. Undervoltage can also occur due to a partially burned contact or a damaged line

As already mentioned, in the known protection arrangements, the area on the motor side is from the power switching element not monitored; the dangers due to errors in this area have not been recognized since then.

The object of the present invention is to provide a motor protection arrangement to create the states deviating from the normal state both on the supply side as also on the motor side of the power switching element

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grasps. The arrangement should also be designed so that detection circuits for detecting the various Parameters are in operative connection with one another through linked contacts in such a way that the system is in operation can be set and is designed to be self-retaining.

This object is achieved according to the invention in that a first protection circuit with a first detection device for detecting a first one for the motor harmful electrical parameters of the power source and with a first tripping device for the power switching element which thereby disconnects the motor from the power source, the first trip device is responsive to the sensing of the first electrical parameter by the first detection device, and wherein a second protection circuit with a second detection device for detecting a second one for the motor harmful electrical parameter is provided on the motor side of the power switching element, with a second tripping device for the power switching element, which thereby separates the motor from the power source, wherein the second triggering device is responsive to the detection of the second electrical parameter by the second detection device appeals to.

The arrangement according to the invention can be designed as a mere protective arrangement, which after triggering in their Starting position can be reset; it can also be designed as an on-off switchgear for the engine be. In both cases, the motor connections are usually connected to a multi-phase circuit and it

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the states (parameters) are recorded in this main circuit.

If the arrangement is only used as a reclosable protective circuit, then a reset pushbutton is required Provided in the protection arrangement, through which a motor protection can be placed in a circuit, so, that after actuation of the main motor switch, the contactor picks up and the motor receives power.

If the protective arrangement is designed as an on-off switchgear, then the reset pushbutton is used as a start button and there is also a stop button intended.

The reset pushbutton is usually a pushbutton with a normally open contact. Closing the Contact closes a control circuit if all are detected by the protective circuit on the network side Parameters are in their correct value range. In this case, a preliminary hold circuit is set by the Reset pushbutton manufactured. The holding circuit also has an additional area, the contacts (or other switching elements) comprises, by detection circuits on the motor side of the power switching element are controlled. If the power switching element is switched on, the holding circuit is activated by the additional area the switching state maintained when all detected on the motor side of the power switching element Parameters are within their target range. A deviation on either side of the power switching element causes the hold circuit to open and thus the power switching element triggered, so the

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The motor supply is interrupted. The additional area of the holding circuit includes normally closed contacts of a Time relay in series with the reset pushbutton and a protective relay that is on the mains side of the protective circuit is provided. Pulling in the protective relay results in a parallel current path to the reset pushbutton and supplies voltage for the power switching element. The closing of the power switch by the engine starting circuit causes a motor-side or a second protective relay to be parallel to the contacts of the timing relay closes if all parameters are in the target range. These latter contacts become independent of it after a predetermined period of time after the closing of the power switching element open, as are the states in the area of the engine-side shift; the timing relay works with a power supply, which is connected to the motor side of the power switching element. The contacts of the timing relay in the hold circuit are required so that the power switching element can be switched on without any signals from the motor side of the power switch exist; the time delay interval must be set so that the normal operating condition can be set and detected on the motor side and the second protective relay has responded, before the timing relay in the hold circuit drops out.

Further details and configurations of the present invention emerge from the following description an embodiment shown in the drawing in connection with the claims.

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BATH ORIGINAL

■ A-40-

A three-phase voltage is applied via lines 1, 2 and fed. The voltage of line 1, afterwards as phase 1, is fed to a line 4, whereas the voltage on line 2, hereinafter referred to as phase 2, a line 6 is supplied.

A hold circuit is connected between lines 4 and 6; it comprises the series connection of a reset pushbutton 7 »a normally closed contact 8 of a timing relay 9, a resistor 11, a diode 12, a coil 15 of a first protective relay 15 and a controllable one Silicon rectifier 14. A storage and delay capacitor 16 is connected in parallel with coil 13; to the Rectifier 14 (thyristor) is a bypass capacitor 17 connected in parallel.

A normally open contact 18 of the first protective relay 15 is connected in parallel to the button 7, whereas a normally open contact 19 of the timing relay 9 is connected in parallel to the normally closed contact 8.

The make contact 18 is the series connection of a lamp 21 and a resistor 22 (together with a Stop contact 55) connected in parallel, a further resistor 23 being connected to the series circuit and all three elements are in series between lines 4 and 6.

Line 3 carries the voltage of phase 3, which is fed to a line 24. The series connection of five Resistors 26, 27, 28, 29 and 31 are connected between lines 4 and 24. Resistance 31 is designed as a potentiometer 32, its wiper

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33 is connected to the line 4 in order to short-circuit an adjustable part of the resistor 31 can. A capacitor 34 is the resistors 28 and 29 as well a part of the resistor 31 connected in parallel; the The connection between the resistors 27 and 28 is via the series connection of a diac 36 and resistors 37 and 38 connected to line 4. The junction between the resistors 37 and 38 is with a Control electrode 39 of the controllable silicon rectifier 14 connected. Finally, there is the junction between resistors 26 and 27 via a capacitor 40 with the connection between the resistor 11 and the normally closed contact 8 or the normally open contact 'B of the Relay 9 or 15 connected.

A lamp 41 is in series with two resistors 42 and 43 to complete the network-side circuit connected between lines 6 and 4; a second break contact 44 of the protective relay 15 is parallel to Series connection of the lamp 41 and the resistor 42.

At the beginning, the reset push button button 7 is pressed and the protective relay 15 is supplied with power, if the controllable silicon rectifier 14 (thyristor) is conductive. So that the thyristor is conductive, neither A mains voltage that is too low may still be missing a phase and the phases of the Tensions be right.

The controllable silicon rectifier 14 is ignited when the voltage across the capacitor 34 is charging reaches a certain value, for example 8 volts, whereby the diac 36 becomes conductive. The capacitor 34 is

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charges itself through resistors 37 and 38 and thereby puts the controllable silicon rectifier into the conductive state. Two conditions must be met for this: The capacitor 34 must achieve the correct charge at the correct point in time. If the voltage is too low, the diac will not fire because the voltage on capacitor 34 does not reach the required 8 volts; or it ignites only at a time when the voltage ^at: silicon controlled rectifier has reversed.

So that the capacitor 34 · is at the correct voltage The minimum required mains voltage must be applied to all three phases. The capacitor 4-0 and the resistor 26 serve as a phase shifter circuit, in which the voltage of phase 2 on line 6 of the Voltage difference between the phase voltages on lines 4- and 24- is added. Is the phase position of all three voltages are correct and the voltages are above a predetermined minimum value, the is adjustable by the potentiometer 32, then the capacitor 34- charged and reaches the ignition voltage of the diac 36 at the right time, whereby the controllable silicon rectifier 14- is ignited.

By igniting the controllable silicon rectifier 14- the protective relay 15 picks up and its normally open contact 18 closes, whereby the reset pushbutton button 7 is bypassed and the lamp 21 is short-circuited (the as a red lamp indicates that the circuit is not in operation). The storage and delay capacitor feeds the coil 13 for a predetermined period of time, whereby the contacts during each half-wave of the alternating

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voltage remain closed, during which the controllable silicon rectifier 14 is non-conductive. Simultaneously the protective relay 15 opens its normally closed contact 44, whereby the short circuit of the lamp 41, a green lamp, is canceled which lights up to indicate that the circuit is working.

The reset pushbutton can now be released; the switching state remains through the normally open contact and maintain the normally closed contact 8 of the timing relay. The timing relay 9 is designed so that it has its contacts opens after a period of time that is required to put the engine side of the system into the operating state after the start bring to.

The protective relay 15 also closes a normally open contact 46, which is in series with a coil 47 of a contactor 48, whose working contacts 51, 52 and 53 with the Lines 4, 6 and 24 are connected, whereby a motor 54 and the circuit on when the contactor 48 is attracted the motor side of the contactor.

If the protection circuit is only used in a reset circuit, then a contact set 50 is added to the circuit the coil 47 is placed so that the arrangement is switched on and off by opening or closing the contact set 50 can be. If, on the other hand, the protective circuit is used in a start-stop circuit for a motor, then the contact set 50 is not needed, but instead, a stop contact 55 is provided in the protective circuit, for example as a breaker on line 6.

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In the protective circuit on the motor side are those Individual parts are provided with the same reference numerals as the corresponding parts, but with a 'added' the line side of the contactor.

The timing circuit comprises a three-phase rectifier 56, at the output of which a smoothing filter is connected is, which comprises the series connection of two resistors 57 and 57 and a filter capacitor 59 and which is a DC voltage on lines 61 and 62 provides. A coil 63 of the timing relay 9 is in series with a controllable one Rectifier 64 between lines 61 and 62 so that when a suitable voltage is applied to an ignition electrode 66 of the rectifier 64, the timing relay 9 is fed and attracts and opens its normally closed contact 8, which is in series with the reset pushbutton used for starting 7 lies.

A time delay circuit 67 is provided to open the normally closed contact 8 from the above Reasons to delay. It should be noted that the normally closed contact 8 of the delay circuit 67 and the normally open contact 19 of a protective relay 15 'on the motor side Error detection circuit are in parallel. The circuit can be maintained if the Normally closed contact 8 is not opened or only opens if the normally open contact 19 was closed beforehand. Will also If a fault is only detected in the circuit on the motor side, the system can only be triggered if the break contact set 8 has been opened. It must therefore be opened both when a contact set 8 The voltage is too low and also when a phase is completely missing. If two phases are missing, it works

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Motor without ^ this not, which means that no damage occurs.

The time delay circuit connects line 61 via resistors 65 and 68 and a capacitor 69 to line 62. The connection between resistors 65 and 68 is connected to line 62 through a variable resistor 71 _5, a series resistor 72 and a capacitor 73 ; Finally, the connection point from resistor 68 to capacitor 69 is connected to line 62 via a resistor 74-.

A programmable unijunction transistor 76 is provided, its collector 77 with the junction between the resistor 72 and the capacitor 73 »its programmable control electrode 78 with the junction of the resistor 68 with the capacitor 69 and its base 79 via series resistors 81 and 82 with the line 62 is connected. A capacitor 83 is connected in parallel with resistor 82 for noise suppression.

The unijunction transistor 76 is therefore used so that a fixed, unchangeable voltage value does not have to be used, but a working voltage must be set which can be selected "tailor-made" for the circuit. The unijunction transistor 76 and the diac 36 are primarily used to To get a suitable timing circuit, because controllable rectifiers are known to have a very low one Have input resistance, which is why they cannot be used well for timing circuits without additional aids

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are. Resistors 71 and 72 and capacitor 73 provide a basic time delay which is within a certain range Limits can be set by the resistor 71. Of the Unijunction transistor 76 has a low ignition threshold, so that it can also be ignited in spite of a voltage that is too low, as it is when a phase is missing or too low Mains voltage can occur «

If the transistor is conductive, the controllable silicon rectifier 64 is ignited at its ignition electrode a noise filter 82, 85 is provided to correct false and too Avoid early ignition if there are significant electrical interference voltages. By igniting of the controllable silicon rectifier 64, the timing relay 9 is fed, which opens its break contact 8. If the normally open contact 19 has not closed, the normally open contacts 51 to 53 are opened and indicate that there is a fault on the motor side. If the normally open contact 19 is closed, the system is working correct and remains under tension

The normally open contact 19 is from the relay 15 'on the motor side Protective circuit controlled. This latter circuit is identical to the corresponding network-side circuit with the exception that the start button 7 and its parallel bridging contact 18 are missing.

A typical circuit consists of the following parts:

Resistances

11 5 kOhm 23 47k0hm 26 82k0hm

27 82 kOhm 28 2.2k0hm 29 470 Ohm

31 1 kOhm 37 22 Ohm 38 1kOhm

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47kOhm Resistances 22kOhm 58 47 ohms 43 470k0hm 57 39kOhm 71 adjustable 67 2OOkOhm 68 200k0hm 81 22 ohms 72 1kOhm 74 82

Capacitors

16 50 / uS ¹ 17 O, o1 / uF 34 0.05 39 0.03J / Ul 59 2yuF 69 0.05 / uF 73 0.33 / uS ¹ 83 1 / reversed silicon rectifiers 14 and 64: C 106 D 1 unijunction -Transistor 76: 2 N 6027 Diac 36: 2 N 4991

The device described can be used with starting systems with partial windings as well as with those with star-delta connection Find use. One, two or three timers and two-phase detection circuits can be used may be required on the motor side of the contactor, with one of the timing elements having a greater delay than that others to detect a preliminary detection of an incomplete transition to the final operating state.

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The circuit can also be used in two-phase systems with no-load or light-loaded circuits. All that needs to be done is to modify the phase shift circuit to provide a phase shift of 90 ° instead of 120 °.

The circuit for detecting undervoltages can also be used as a circuit for detecting overvoltages if the timing circuit is changed so that the controllable rectifier does not ignite in the event of an overvoltage he follows. If controllable rectifiers connected in series are used, then an overvoltage as well as undervoltage protection can be achieved. A general arrangement may include a Detector for detecting two-phase, three-phase or multi-phase voltage imbalances, the the contactor trips when the voltage imbalances exceed a specified level. In the same way a detector can also be inserted in the motor protection circuit are detected, the inequalities of a two-, three- or multi-phase current.

It goes without saying that other functions can also be realized with the circuit, in the corresponding i ^ hlschalter can be added to control additional controllable rectifiers. Will the controllable rectifiers are used in separate circuits instead of having them in series or in parallel with each other switch, then the contacts of the protective relays on the motor side of the system are all connected in series to one another * - tet and the normally closed contact 8 of the timing relay is parallel to this series circuit.

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Claims (11)

Claims Λ . / Arrangement for protecting electric motors which can be connected to a power source via a power switching element, characterized by a first protective circuit with a first detection device for detecting a first electrical parameter of the power source that is harmful to the motor and with a first triggering device for the power switching element that controls the motor from the power source when the first tripping device responds to the detection of the first electrical parameter by the first detection device, and by a second protective circuit with a second detection device for detecting a second electrical parameter harmful to the motor on the motor side of the power switching element and with a second trip device for the power switching element, which disconnects the motor from the power source when the second trip device is responsive to the detection of the electrical parameter by the second detection device. 2. Arrangement according to claim 1, characterized in that the first electrical parameter is a group electrical parameters, and that the first triggering device by the first detection device can be triggered when detecting at least one of the electrical parameters of the first parameter group is. 1300U / 1058 3. Arrangement according to claim 1 or 2, characterized in that the second electrical parameter is a group electrical parameters, and that the second triggering device by the second detection device can be triggered when detecting at least one of the electrical parameters of the second parameter group. 4. Arrangement according to one of claims 1 to 3, characterized characterized in that the first and second parameters are the same. 5. Arrangement according to one of the preceding claims, characterized in that the second triggering device is in operative connection with the first triggering device, the first triggering device can be actuated by the second triggering device. 6. Arrangement according to one of the preceding claims, characterized in that the power switching element is a contactor. 7 · Arrangement according to one of the preceding claims, characterized in that it has a timing element and Means for delaying the effect of the second tripping device on the opening of the power switching element has during a predetermined period of time. 8. Arrangement according to one of the preceding claims, characterized in that the power source is a Multi-phase AC power source and the electric motor is a multi-phase motor. 130014/1058 * ^A 9. Arrangement according to one of the preceding claims, for electrical power sources with more than two Lines, characterized in that the first detection device is the first triggering device provided for detecting electrical parameters at the connection between the power switching element and the motor and the release device responds when a " electrical parameters by the detection device, and that the detection device has more is fed as two lines from the power source and includes means for detecting a substantial one Power reduction in one of the power supply lines, whereby the power switching element can be triggered is. 10. Arrangement according to one of the preceding claims, characterized in that the second protective circuit with the second detection device for detecting electrical ones that are harmful to the engine Parameters of the power source and the second triggering device for triggering the power switching element serves to thereby disconnect the motor from the power source, wherein the second trip device upon detection of an electrical parameter harmful to the engine by the second detection device responds and the first tripping device through the second protective circuit in operative connection with the power switching element and this triggers to disconnect the motor from the Power source. 1300U / 1058 11. Arrangement according to one of the preceding claims, characterized in that the load is a single-phase or multi-phase load with an active and / or reactive component is. 1300U / 1058